In medical practice, respiratory assistance devices, such as artificial respirators are in use. The respiratory assistance devices employ methods such as a controlled ventilation (Controlled Ventilation) method used for a patient in the absence of spontaneous breathing (a patient under general anesthesia, during cardiopulmonary resuscitation, or in a critical condition), an assisted ventilation (Assisted Ventilation) method for creating a positive pressure in a respiratory tract in accordance with the spontaneous breathing of a patient, a partial assisted ventilation (Assist/Control) method using the assisted ventilation and the controlled ventilation in combination, and a high frequency oscillation ventilation method for realizing a very small amount of a single ventilation of 1 to 2 ml/kg by causing a gas supplied by an respiratory tract to oscillate at a frequency of 5 to 40 Hz.
The respiratory assistance device is used also for a patient with a respiratory disorder during sleep. This respiratory disorder is caused by the blockage of a respiratory tract as a result of relaxation of the muscle of the respiratory tract during sleep and the resultant retraction of the posterior part of a tongue or a soft palate. Creating a positive pressure in a respiratory tract alleviates the symptom of a patient with this type of respiratory disorder.
Any of the respiratory assistance devices requires a pump unit for creating a positive pressure in a respiratory tract. A blower that transports a gas by the rotation of a fan, a cylinder pump that transports a gas by the reciprocal motion of a piston, or the like is used as a power source for this pump unit.